Dipeptidylpeptidase IV (DPPIV) is a kind of serine protease that specifically hydrolyzes a dipeptide of Xaa-Pro or Xaa-Ala (where Xaa may be any amino acid) from the N terminus of a polypeptide chain.
There are various reports regarding the role of DPPIV (also called to as CD26) in the body and its relationship with diseases (Holst, et al., Diabetes, Vol. 47, pp. 1663-1670, 1998; Augustyns, et al., Current Medicinal Chemistry, Vol. 6, pp. 311-327, 1999; Meester, et al., Immunol. Today, Vol. 20, pp. 367-375, 1999; and, Fleicher, et al., Immunol. Today, Vol. 15, pp. 180-184, 1994).
GLP-1 (glucagon-like peptide 1) is a peptide hormone that mainly acts in the pancreas after being secreted from the lower small intestine after meals, and primarily has the function of amplifying glucose-induced insulin secretion. In addition, there are several reports suggesting that GLP-1 has an appetite-suppressing action. DPPIV hydrolyzes GLP-1, forming an inactive or antagonistic peptide.
Substances that inhibit the enzyme activity of DPPIV enhance the insulin secretion response to oral glucose loading by enhancing the action of intrinsic GLP-1, thereby improving impaired glucose tolerance.
Consequently, DPPIV inhibitors are considered to be useful for the prophylaxis and treatment of diabetes (particularly type 2 diabetes), etc. Also, they are expected to be effective for the prophylaxis and treatment of other diseases induced or exacerbated by impaired glucose tolerance (including hyperglycemia (such as postprandial hyperglycemia), hyperinsulinemia, diabetes complications (such as renal disorder and neurological disorder), lipid metabolism disorder and obesity, etc.).
Moreover, DPPIV inhibitors are also expected to be effective for the prophylaxis and treatment of diseases that are to be improved by enhancing the appetite-suppressing action of GLP-1 (including overeating and obesity, etc.).
Also, DPPIV (CD26) present on the surface of T cells is strongly upregulated following T cell activation, and plays an important role in the activation and proliferation of T cells. T cell activity is known to be suppressed when DPPIV (CD26) is blocked by antibodies or inhibitory substances. Also, there has been an interest in the correlation between this enzyme and the pathological state in collagen metabolism disorders and diseases associated with abnormal immunity. For example, the DPPIV (CD26) positive rate of peripheral blood T cells is elevated in rheumatoid patients, and high levels of DPPIV activity have been detected in the urine of nephritis patients. Moreover, DPPIV (CD26) is also thought to play an important role in the entry of HIV into lymphocytes.
Consequently, substances that inhibit DPPIV (CD26) are expected to demonstrate prophylactic and therapeutic effects against diseases including autoimmune diseases (such as arthritis and rheumatoid arthritis), osteoporosis, acquired immunodeficiency syndrome (AIDS) and rejections of transplanted organs and tissues.
On the other hand, as compounds having DPPIV inhibitory action, there are described 2-cyanopyrrolidine derivatives having DPPIV inhibitory action in International Patent Laid-Open Publications Nos. WO98/19998 and WO00/34241.
The present invention provides a novel aliphatic nitrogen-containing 5-membered ring compound having an excellent DPPIV inhibitory action.